The present invention relates to a process for manufacturing TFT liquid crystal displays and, more specifically, to a process for manufacturing pixel electrodes with rough diffuser surfaces for serving as the reflection members of TFT-LCD devices.
With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in electrical products, such as PDAs, laptops, cell phones, high resolution television sets, etc. due to advantages as smaller size, portability, and lower power consumption. Particularly the up-to-date reflective LCD device is usually performed by utilizing the reflection of light incident from outside, wherein the pixel electrodes made of metal materials are applied to serve as reflection members. Thus the light reflected form the pixel electrodes performs desired images on the displays through liquid crystal molecules and color filters. The reflective type liquid crystal display which does not require a backlight has been vigorously developed because these type of displays are power saving, thin and lightweight. In addition, since members for the backlight are not necessary, the cost may be reduced.
Notedly, the deeply concerned and important key point is how to promote efficiency of light reflection because the light source of the reflective type LCD comes from the external illumination. In prior art, polarizing plates are introduced to adjust the phases of incident lights for increasing reflection intensity. However, it is not practical to apply the additional polarizing plates into the reflective type LCD. Another solution is to fabricate the pixel electrodes with rough surface for serving as the reflection diffusers for completely utilizing external illuminations, promoting efficiency of reflections and increasing contrasts.
Please refer to FIG. 1, the cross-sectional view of TFT-LCD with rough reflection fabricated by prior art is shown. The related process comprises follow steps. A gate structure 12 is defined on a glass substrate 10 first. Then an insulating layer 14 is deposited on surfaces of the gate structure 12. A semiconductor layer 16 such as amorphous silicon, a doped silicon layer 18 and a metal layer are sequentially formed on the gate structure 12. Next a photolithography procedure is performed to define a drain structure 20 and a source structure 22. After the TFT-LCD 24 is fabricated, an additional step is performed to form plural bumps 26 made of photoresists in the areas for defining pixel electrodes. Next a passivation layer 28 such as polymer material is coating on the bumps 26. And a pixel electrode 30 is formed above those layers. Thus, the reflection efficiency is promoted due to the pixel electrode 30 having a rough and uneven surface.
FIG. 2 illustrates the typical method for fabricating the bumps 26. First, an insulating photoresist layer is deposited on the substrate 10, following defining a plurality of photoresist bumps 25 by proceeding photolithography and etching procedures. Then the reflow step is performed to make topography of the photoresist bumps 25 become much smoother, as hemi-spherical bumps 26 indicated in FIG. 3. Wave-like surfaces are continuously formed by depositing foregoing passivation layer 28 on the substrate 10 to cover the bumps 26 uniformly. After that, another photolithography procedure is then performed to form contact hole in the passivation layer 28 to expose partial surface of drain structure 20. At the last, the pixel electrode 30 is deposited to make electrical connection with source structure 20.
Notedly, it is needed to proceed two depositions of material layer (including photoresist layer and following passivation layer). The photolithography and etching procedures are also required to be carried out twice. Therefore the cycle time of the process is prolonged and the complexity increases markedly which cause production reduced.
The first objective of the present invention is to provide a method for manufacturing a TFT-LCD device having pixel electrodes with rough surfaces for serving as reflection members.
The second objective of the present invention is to provide a method for forming pixel electrodes with rough surfaces, wherein the wave-like surfaces are defined on the photosensitive insulating passivation layer by performing a defocused exposing procedure.
The third objective of the present invention is to provide a method for forming a contact hole and the wave-like surfaces simultaneously on the photosensitive insulating passivation layer by performing a patterning procedure using defocused light.
A method of forming a TFT-LCD device with a rough pixel electrode for serving as the diffuser member is disclosed hereinafter. The method comprises the following steps. First, a gate structure is defined on a transparent insulating substrate, following an insulating layer is deposited on the gate structure and the transparent insulating substrate. Next, a semiconducting layer is formed on the insulating layer. And an etching stopper is defined on the semiconducting layer. A drain structure and a source structure are then fabricated at the side walls of the etching stopper.
Subsequently, a photosensitive insulating passivation layer is formed on the transparent insulating substrate to cover the drain structure and the source structure. The photosensitive insulating passivation layer is then patterned using defocused light. The mask introduced in above patterning step has plural patterns of the independent spots and a contact hole pattern thereon. The distance between two adjacent independent spot patterns is smaller than the resolution of exposure system, while the distance between the adjacent independent spot pattern and the contact hole pattern is larger than it.
The exposed photosensitive insulating passivation layer is then developed to have the wave-like surfaces and the contact holes thereon. After that, a pixel electrode is formed finally on the photosensitive insulating passivation layer to electrical connect to the drain structure. The pixel electrode rises and falls with the surfaces of the photosensitive insulating passivation layer to have a rough diffuser surface.